Porous particulate materials carrying catalytically active elements are known in the art. These materials are useful in many processes, such as treating petroleum cuts or treating effluents, e.g., catalytically converting the exhaust gases emanating from internal combustion engines.
The catalysts typically comprise a carrier produced by shaping a porous material such as alumina. Thus, the carrier may assume various shapes, such as spheres, cylindrical extrusions or extrusions having a polylobal cross-section or a cross-section of various shapes, such as a wheel.
The porous materials generally used are alumina, silica, zeolites or the like. These carriers generally have a large specific surface area, e.g., over 20 m2/g, to provide a large surface area which is rendered catalytically active by depositing catalytically active elements thereon.
Various elements are, typically, impregnated into the porous material. For instance, U.S. Pat. No. 5,232,889 is directed to a catalyst prepared by impregnating a porous material, preferably alumina spheres, with a colloidal dispersion of a metal to be deposited. The colloidal dispersion must have a particulate size no greater than the pore size of the porous material. When the colloidal dispersion penetrates the pores of the carrier, the reactive surface locations of the carrier change the pH of the dispersion, causing the metal to be deposited within the porous material. U.S. Pat. No. 6,040,265 is also directed to impregnating a porous material, such as alumina or zeolites, with a solution of a primary metal acetate, at least one secondary metal acetate and an organic depositing reagent such as a soluble sugar, saccharides, polysaccharides, or derivations thereof, thereby forming an impregnated porous material. In addition, Canadian Patent 2,033,291 is directed to a catalyst for the conversion of nitrogen oxides in a high-temperature exhaust gas. The catalyst consists of a zeolite (the molar ratio of SiO2/Al2O3 is >20) that contains 0.5-10 wt % cerium oxide. The catalyst can be prepared either by impregnating the zeolite with an aqueous solution of a nitrate, a halide or a sulfate of cerium, or it can be prepared by effecting ion exchange. The mixture is then dried and calcined at 300-600° C.
The prior art also shows that other elements may form an aggregation with porous material to produce a catalytic material. For instance, U.S. Pat. No. 5,804,526 is directed to an adsorbent that exhibits an excellent adsorption ability for nitrogen oxides. The adsorbent can be made up, for example, of an aggregate of cerium oxide and zeolite. The content of cerium oxide in the catalyst is in the range of 10% to 80% by weight based on the total equivalent zeolite and cerium oxide content. The adsorbent is made from a mixture of cerium oxide crystallite particles and zeolite particles of dealuminized ZSM-5 zeolite, wherein the cerium oxide crystallite particles are comprised of polycrystalline aggregates having an average crystalline grain size of less than 500 Å. As an aggregate, the cerium oxide crystallite particles are adjacent to surfaces of the zeolite particles.
There are several patents that disclose the use of a catalytic coating on a porous metallic, or similar, support for the abatement of gases. U.S. Pat. No. 4,900,712 relates to the adsorption of one or more catalytically active oxides onto high surface area alumina. The method of preparing the catalytic coating involves the use of a colloidal deposit approach to uniformly dope oxides on high surface area alumina. The colloidal dispersions are prepared by taking an aqueous solution of a metal nitrate salt and converting the metal nitrate salt to a metal oxide colloid with an ion-exchange resin. The colloidal dispersion of the oxide is slurried with alumina, wherein the colloidal oxide particles are adsorbed onto the alumina. In order to maintain the adherence of the catalytic coating on the support and to ensure maintenance of a high surface area on the catalyst the doping oxide was limited to less than about 20% by weight, based on the total equivalent alumina and doping oxide content.
U.S. Pat. Nos. 5,431,887 and 5,556,819 are directed to flame-arresting coated filters for use in catalytic broiler smoke abatement assemblies. The filter is coated with a slurry of alumina (zeolite may be used or a mixture of the two) and colloidally dispersed ceria; the ceria acting as a binder. The colloidal dispersion of ceria was made using high temperatures for extended periods of time, as described in the aforementioned U.S. Pat. No. 4,900,712.
There is, however, a need for a process that provides a stable free-flowing bulk catalytic metal oxide-coated microporous particulate material with a variety of loadings and obviates the shortcomings of the prior art.